1. Field of the Invention
The present invention relates to mosaic ink recorders, and in particular to a transducer structure for such a recorder.
2. Description of the Prior Art
Mosaic ink recorders are known, such as the recorder described in German OS No. 2,527,647, for ejecting recording liquid droplets from a plurality of nozzles in a recording head onto a moving recording medium for punctiform representation of alphanumeric characters and images wherein each nozzle has a piezoelectric transducer associated therewith which is in the form of a tooth of a comb-like piezoplate. The piezoelectric transducers have free ends which respectively overlay the recording head nozzles. The transducers are normally connected to a potential source of appropriate polarity and move to eject a liquid droplet from the associated nozzle upon interruption of the potential. The piezoplate of which the transducer teeth are a part is bilaminar and consists of a layer of piezoceramic material and a layer of carrier material.
Such conventional recorders exhibit the problem that, upon activation of an individual transducer tooth, cross-talk between the activated transducer tooth and adjacent transducer teeth may occur as a result of hydraulic coupling through the recording liquid. This coupling may cause an adjacent non-activated tooth to be set in motion and thus expel recording liquid from the nozzle associated therewith, thus causing an unwanted dot to be printed on the recording carrier.
A further problem resulting from hydraulic coupling which is present in conventional recorders, to which the problem of mechanical coupling between adjacent transducers also contributes, is the necessity of maintaining each transducer tooth prior to its activation in a rest or non-operating position in order to obtain a good recording quality. If two adjacently disposed transducer teeth are to be activated in direct succession, the first-activated tooth should not set the adjacent tooth in oscillation, even if the unwanted oscillation of the adjacent tooth does not cause recording liquid to be ejected. In conventional recorders, this problem is attempted to be solved by insuring that the time interval between successive activation pulses is sufficiently long so that the oscillation of a tooth adjacent to an activated tooth decays sufficiently before actuation of the adjacent tooth. The result is a significant reduction in the maximum recording speed. The oscillation of the adjacent tooth may also be effectively attenuated by utilizing a recording liquid of high viscosity, however, this solution increases the hydraulic coupling between the transducer teeth.
The oscillation speed of a transducer tooth is greatest at the tip of its free end, and therefore the hydraulic coupling between the teeth is also greatest in the region of the tips of the transducer teeth. Another possibility for reducing the hydraulic coupling between adjacent teeth is to increase the physical spacing between the transducer teeth. This attempted solution, however, reduces the recording quality because the distance between the nozzles associated with the transducer teeth must necessarily be increased as well.